1. The Field of the Invention:
The present invention generally relates to a gas sensor control unit for electrically connecting plural gas sensors with an external apparatus such as an ECU (engine control unit). The plural gas sensors detect and transmit via the gas sensor control unit gas concentration signals of specific gas components exhausted from an internal combustion engine to the external apparatus for controlling fuel-combustion in the engine. In particular, the present invention relates to a gas sensor control unit capable of transmitting gas-detection signals detected by plural gas sensors and internal resistance signals thereof to the external apparatus for controlling an air/fuel ratio of an internal combustion engine, the plural gas sensors each comprising a gas-sensing solid electrolyte cell element.
2. Description of the Related Art:
A conventionally known gas sensor control unit adapted for connection to a gas sensor comprises a gas-sensing solid electrolyte cell, which unit detects a gas detection signal corresponding to a specific gas concentration (e.g., oxygen concentration) of an exhaust gas exhausted from an internal combustion engine and also detects an internal resistance signal corresponding to an internal resistance of the gas sensor element. The gas sensor control unit then outputs these signals to an engine control unit (ECU), as disclosed in Patent Documents 1 and 2.
The external apparatus performs various control functions including air/fuel ratio feedback control of the internal combustion engine and target temperature control of the gas sensor element, based on the gas detection signal and the internal resistance signal transmitted from the gas sensor control unit connected with the gas sensor.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. H10-0814140 (FIGS. 1 and 10)
[Patent Document 2] Japanese Patent Application Laid-Open (kokai) No. H10-048180 (FIG. 2)
3. Problems to be Solved by the Invention:
Conventionally, one known gas sensor control unit is provided for each gas sensor. In other words, a conventional gas sensor control unit is only capable of controlling or processing signals from a single gas sensor. Thus, when plural gas sensors are mounted in exhaust pipes of both cylinder banks as in a V-type engine compartment so as to accurately control an air/fuel ratio of the internal combustion engine, it is necessary to install plural gas sensor control units, depending on the number of gas sensors to be provided in the engine compartment.
Therefore, the use of plural gas sensor control units connecting plural gas sensors with an external apparatus causes an installation space problem in accommodating plural gas sensor control units in a space-limited engine compartment and an increase in cost. In addition, when plural gas sensor control units are installed in the engine compartment, an increased number of signal paths in a wiring harness between the plural gas sensor control units and the external apparatus becomes disadvantageously complicated. This is because every gas detection signal and every internal resistance signal of the plural gas sensors detected by the plural gas sensor control units is outputted to the external apparatus.